Blender 2.7 Basic Vertex question
If I understand you're meaning correctly, you want to add vertices only on a specific edge, and not to add an entire loop.

To do that, select the edge, then subdivide using the button on the Tools Panel, or the shortcut W --> Subdivide. You can then edit the number of subdivisions through the Last Operator Panel (bottom of the Tools Panel), or the F6 menu.